Temporomandibular joint (TMJ) clicking is the commonest sign of mandibular dysfunction and is considered by some to be pathologic or potentially harmful. Correction of occlusal problems is sometimes considered important in helping to re-establish a proper condyle-disc relationship and orthodontic therapy is sometimes recommended. Conversely TMJ clicking may arise during or after orthodontic therapy possibly due to occlusal changes or the effects of mechanics of the TMJ. TMJ clicking in approximately 50 pre-orthodontic patients will be recorded on paper tape for in depth analysis of the character of the sound. Simultaneous videotape recording of jaw movements will permit analysis of the timing of the sound. The static occlusion will be analysed on study models and the functional occlusion will be assessed clinically. Another group of 50 pre-orthodontic patients without clicking will be evaluated longitudinally in a similar way. The data wil be recorded prior to, after 6 months and 12 months of treatment in both the clicking and non-clicking groups. A cross-sectional study on approximately 30 patients with clicking and 30 without clicking will be done at the end of active orthodontic treatment and two years post-treatment to complement the longitudinal pilot study. Associations between various malocclusion characteristics and orthodontic mechanotherapy, with the presence, onset or resolution of various types of TMJ sounds will be explored using appropriate statistical analyses.